Iodine based preparations are commonly accepted as among the most effective of the available germicides. In addition, solution of iodine have been shown to possess fungicidal and viricidal properties. Iodine solutions appear to exhibit no selectivity against different strains of bacteria, all types being killed at approximately the same level of concentration and exposure time.
Numerous mixtures of iodine are now available. These include tincture of iodine, iodoform, iodine trichloride and the various iodophores. Of the available embodiments of iodine, the iodophores are in most common use and presently occupy the position of greatest interest.
The prior art teaches that crystalline iodine can be placed in solution through the use of surfactants such as polyvinyl-pyrrolidone, polyethoxyethanol derivatives and a variety of the quaternary ammonium compounds. These resulting mixtures of iodine and surface active agents are referred to in the scientific literature as iodophores.
Iodophore solutions are polar and micellar in character. Given that iodine is very insoluble in polar water, the problem of solubilization is partially solved in preparing iodophores by placing cystalline iodine in a micellar system. In effect, iodine is solubilized and carried in micellar aggregates which are formed through the use of surfactants. The micellar system acts as a reservoir which liberates iodine into the polar water and thence onto the surface to be treated.
It should be noted that iodophore mixtures exhibit maximum activity and stability in solutions, the pH of which must be within the range of 3.0 to 4.0. Solutions of iodine outside of this range show reduced stability and activity.
The use of surfactants to solubilize crystalline iodine only partially solves the problem of embodying non polar iodine in polar water. Investigation of the commercially available iodophores indicates that the inherent instability of iodine in polar water is not remedied in manufacture of these products. On analysis, iodophores are found to be complexes of indefinite components; ie. they are comprised of mixtures of all possible oxidative states of iodine. Further evidence of the instability of the iodine in iodophore preparations is found in the fact free iodine is eventually precipitated from such compositions. Moreover, when iodophores are evaporated to dryness on the skin surface for example, it is found that the individual component chemicals, ie. free iodine, free salts and surfactants are released onto the treated surface. Given the known irritant and toxic effects of free iodine and the reported carcinogenic potential of surfactants such as poly-vinylpyrrolidone, iodophore preparations would appear to have the possibility of exerting significant adverse effects.
(References: Ashwood-Smith, M. J. Polyvinyl-pyrrolidone Solutions used in Plasma Expanders; Potential Carcinogens. Lancet, 1, 1304, (1971).
Towers, R. P. Lymph Node Changes due to Polyvinyl-Pyrrolidone, Jour. of Clin. Pathology 10, 175-177, (1957).